Main Difference
The main difference between Efficacy and Effectiveness is that the Efficacy is a able to finish something satisfactorly and Effectiveness is a capability of producing the desired result
Efficacy
Efficacy is the ability to get a job done satisfactorily. The word comes from the same roots as effectiveness, and it has often been used synonymously, although in pharmacology a distinction is now often made between efficacy and effectiveness. The word efficacy is used in pharmacology and medicine to refer both to the maximum response achievable from a pharmaceutical drug in research settings, and to the capacity for sufficient therapeutic effect or beneficial change in clinical settings.
Effectiveness
Effectiveness is the capability of producing a desired result or the ability to produce desired output. When something is deemed effective, it means it has an intended or expected outcome, or produces a deep, vivid impression.
Efficacy (noun)
Ability to produce a desired effect under ideal testing conditions.
Efficacy (noun)
Degree of ability to produce a desired effect.
Effectiveness (noun)
The property of being effective, of achieving results.
“The effectiveness of the drug was well established.”
Effectiveness (noun)
The capacity or potential for achieving results.
Effectiveness (noun)
The degree to which something achieves results.
“He questioned the effectiveness of the treatment.”
Efficacy (noun)
the ability to produce a desired or intended result
“there is little information on the efficacy of this treatment”